1. Field of the Invention
This invention generally relates to a water vessel and in particular to a catamaran including a submerged connection member connecting a pair of floats or hulls.
2. Description of the Prior Art
A catamaran typically includes a pair of hulls or floats which are joined by a deck or some other connecting structure bridging between them. However, such a connecting structure normally extends in the air and not submerged under the water. In the past, the present inventor invented a working catamaran including a pair of floats joined by a submerged connecting member for use in collecting solid floating materials on the water surface as disclosed in the Japanese Utility Model Post-examination Publication No. 57-18238. The working catamaran disclosed in this publication is illustrated here as FIGS. 4a through 4c. As shown in these figures, the working catamaran generally indicated by numeral 1 includes a pair of floats or hulls 2. In the illustrated structure, a bow tip end 3 of each of the floats 2 is located toward well 4, which is a region sandwiched between the floats 2 spaced apart from each other, with respect to its longitudinal center line CL. And, each of the floats 2 has a substantially vertical inner side wall at its bow portion a, intermediate portion b and stern portion c. In particular, the inner side walls b of the opposite floats 2 extend substantially in parallel each other and with respect to the longitudinal center axis CL of each of the floats 2.
A connecting member 5 extends between the opposite inner side wall surfaces a of the floats 2 at those portions d that are submerged under water. The connecting member 5 is fixedly attached at each end to the floats 2 so as to provide an increased structural integrity. Because of the provision of this connecting member 5, the floats 2 may be spaced apart at a greater distance than otherwise possible. This is particularly important in such a working vessel since it allows to sweep a wider water surface. As shown in FIG. 4b, the connecting member 5 is defined as a waterfoil having a particular cross sectional shape. That is, the connecting member 5 includes a curved bottom surface 5a which extends from the bow end downwardly until it hits the bottom of the float 2 with increasing its radius of curvature, and, then, extends along the bottom of the float 2 until it reaches its downstream end 5c. The curved portion of the bottom surface 5a extends generally from the forward end of the submerged inner side wall surface portion d to the bottom e of the bow portion a, whereby a space 5d having a generally triangular-shaped cross section is defined below the bottom surface 5a. The connecting member 5 also includes a curved top surface 5b which first extends substantially horizontally from the bow end over a predetermined distance and then extends downwardly toward the downstream end 5c with its radius of curvature gradually increasing. The particular shape of the connecting member 5 as described above is advantageous in providing stability while the working catamaran is in operation.
As also shown in FIG. 4b, a rotating impeller 7 is disposed above the connecting member 5 and extending between the opposite floats 2. And, thus, as the working catamaran 1 cruises, any solid materials floating on the water surface is first trapped in a mouth between the opposite floats 2 and then driven into the downstream portion of the well 4 defined between the opposite floats 2 by means of the rotating impeller 7. Also provided is a deck 6 extending between the floats 2 and in the air, which provides a working area for an operator and a bridge or operating room may be provided on the deck 6.
Thereafter, the present inventor improved the catamaran disclosed in the above publication so as to allow to collect oil spills rather than solid floating materials and filed a Japanese Patent Application, No. 58-29378, and also a U.S. patent application, Ser. No. 582,199, which has been issued as U.S. Pat. No. 4,551,244, which is hereby incorporated by reference. This improved catamaran also includes a connecting member which is similar in many respects to the connecting member 5 illustrated in FIGS. 4a through 4c and described above.
As described above, the working catamaran provided with a submerged connecting member is advantageous in attaining stability in operation and such a submerged connecting member also has some merits in providing stability while cruising particularly through rough waters. However, it has been found that the bow end tends to become submerged under water when the working catamaran cruises at a relatively high speed. Since there are those cases in which the working catamaran is required to cruise at a relatively high speed so as to reach a site as soon as possible so that a collecting operation can be carried out immediately, it is also important that the working catamaran can cruise at a relatively high speed without problems. However, in the prior art structure, since the bow end tends to become submerged when the cruising speed increases, there has been an upper limit in the cruising speed. According to the experiments conducted by the present inventor, it has been found that a catamaran having a structure described above has a tendency to cause its bow end to be submerged under water when its cruising speed is increased even if the connecting member 5 has been removed. Therefore, there is an upper limit in the cruising speed for such a catamaran irrespective of whether it is provided with a connecting member or not.